1. Field of the Invention
This invention relates generally to the field of restoral of dedicated data communications links using Public Switched Digital Service (PSDS) facilities. More particularly, this invention relates to a method of achieving such dial restoral which utilizes telephone company central office facilities for digital bridging and requires minimal equipment and dedicated lines at a customer's premise.
2. Background of the Invention
Large data communication networks using digital telephone lines are commonly used to transfer information in government and many industries such as banking and airlines. Most commonly, the main circuits of such networks are dedicated circuits which are owned or leased by the customer from the telephone companies. When failures of access devices (modems, digital service units, etc.) or telephone circuits occur, such networks generally require backup to assure a continuous flow of information.
When such circuits are largely made up of modems or other relatively low speed access devices, backup is commonly done by dial-up circuits which replace the affected circuits end-to-end. Even with low speed circuits, dial up modem speeds are often too slow to adequately back up and restore the network at full speed. With digital circuits, the use of dial backup presents even greater problems due to the great discrepancy in throughput of information between the normal digital circuits and analog dial circuits.
When digital multipoint or digital multiport multipoint circuits (as disclosed in U.S. patent application Ser. No. 07/513,392, filed Apr. 20, 1990 to Basnuevo et al, issued as U.S. Pat. No. 5,177,739, which is incorporated herein by reference) require back up, the complexity grows even further. In order to adequately perform such backup functions with known technology, digital bridging is required along with multiple backup access devices and switching devices, all of which are generally purchased or leased by the customer and must be maintained at the customer's property. The complexity and expense required for such a scheme is often prohibitive.
The present invention provides a method for backing up digital circuits using Public Switched Digital Services (PSDS) which requires minimal additional hardware at the customer's location and utilizes central office digital bridging to provide full speed backup to digital networks.